1. Field of the Invention
The present invention relates to a light source.
We have developed technology for the production of light via plasma excitation in a Lucent Waveguide electromagnetic Wave Plasma Light source. We refer to this technology as LUWPL technology.
2. Description of the Related Art
We define a LUWPL source as having:                a fabrication of solid-dielectric, lucent material, having;                    a closed void containing electro-magnetic wave, normally microwave, excitable material; and                        a Faraday cage:                    delimiting a waveguide,            being at least partially lucent, and normally at least partially transparent, for light emission from it,            normally having a non-lucent closure and            enclosing the fabrication;                        provision for introducing plasma exciting electro-magnetic waves, normally microwaves, into the waveguide;the arrangement being such that on introduction of electro-magnetic waves, normally microwaves, of a determined frequency a plasma is established in the void and light is emitted via the Faraday cage.        
In our so-called “LER” patent application No. EP2188829, there is described and claimed (as granted):
A light source to be powered by microwave energy, the source having:
                a body having a sealed void therein,                    a microwave-enclosing Faraday cage surrounding the body,                        the body within the Faraday cage being a resonant waveguide,        a fill in the void of material excitable by microwave energy to form a light emitting plasma therein, and        an antenna arranged within the body for transmitting plasma-inducing, microwave energy to the fill, the antenna having:                    a connection extending outside the body for coupling to a source of microwave energy;wherein:                        the body is a solid plasma crucible of material which is lucent for exit of light therefrom, and        the Faraday cage is at least partially light transmitting for light exit from the plasma crucible,the arrangement being such that light from a plasma in the void can pass through the plasma crucible and radiate from it via the cage.        
As used in Our LER Patent:
“lucent” means that the material, of the item which is described as lucent, is transparent or translucent—this meaning is also used in the present specification in respect of its invention;
“plasma crucible” means a closed body enclosing a plasma, the latter being in the void when the void's fill is excited by microwave energy from the antenna.
One alternative to the LER technology is our so-called “Clam Shell”, which is the subject of our International Patent Application No PCT/GB08/003811. This describes and claims (as published):
A lamp comprising:
                a lucent waveguide of solid dielectric material having:                    a bulb cavity,            an antenna re-entrant and            an at least partially light transmitting Faraday cage and                        a bulb having a microwave excitable fill, the bulb being received in the bulb cavity.        
The fabrication of a LUWPL can be of continuous solid-dielectric material between opposite sides of the Faraday cage (with the exception of the excitable-material and closed void) as in a lucent crucible of our LER. Alternatively it can be effectively continuous as in a bulb in a bulb cavity the “lucent waveguide” of our Clam Shell. Alternatively again fabrications of our International patent application no. PCT/GB2011/001744 and other as yet unpublished applications on improvements in our technology include insulating spaces distinct from the excitable-material, closed void.
Accordingly it should be noted that whereas terminology in this art, prior to out LERs, includes reference to an electroplated ceramic block as a “waveguide” and indeed the lucent crucible of our LER has been referred to as a “waveguide”. However in the this specification, we use “waveguide” to indicate jointly:                the enclosing Faraday cage, which forms the wave guide boundary, and        within the cage, the fabrication including its solid-dielectric lucent material and the void, which material influences the manner of propagation of the waves inside the cage.        
Further in our International Patent Application No. PCT/GB2010/000911, there is described and claimed (as published):
A light source to be powered by microwave energy, the source having:
                a solid plasma crucible of material which is lucent for exit of light therefrom, the plasma crucible having a sealed void in the plasma crucible,        a Faraday cage surrounding the plasma crucible, the cage being at least partially light transmitting for light exit from the plasma crucible, whilst being microwave enclosing,        a fill in the void of material excitable by microwave energy to form a light emitting plasma therein, and        an antenna arranged within the plasma crucible for transmitting plasma-inducing microwave energy to the fill, the antenna having:                    a connection extending outside the plasma crucible for coupling to a source of microwave energy;the light source being characterised by the inclusion of:                        a source of microwaves at a frequency to excite resonance within the lucent crucible and the Faraday cage for excitation of a light emitting plasma in the sealed void and        a waveguide for coupling microwaves from the generator to the antenna, the waveguide being:                    substantially two or more half wave lengths long and having:                            a waveguide input from the generator positioned close to an input end of the waveguide and                a waveguide output to the antenna connection positioned close to an output end of the waveguide.                                                
Herein we refer to the generator-to-antenna waveguide as a “transition waveguide”.
In our International patent application No PCT/GB2010/001518, we have described and claimed:
A luminaire having:                a plasma light source powered by High Frequency (HF) power;        a HF power supply having a physical structure,                    the light source and the HF-power-supply physical structure being connected together as an assembly;                        a housing for the HF power supply, the said assembly and the housing being fastened together and the housing having:                    an aperture through which the said assembly extends with cooling air flow clearance and            a cooling air fan arranged at an opening in the housing for drawing air in (or out) for cooling of the HF power supply and passage out (or in) via the aperture and past the light source; and                        a reflector for at least substantially collimating light from the light source fastened to the housing at the aperture and the reflector having its own aperture through which the said assembly extends, with the light source arranged within the reflector.This was drafted before we defined a LUWPL. We refer to this luminaire as “our First Luminaire”. It was intended to include an LER LUWPL.        
We have also applied for patents on the drive circuitry for the magnetron which is central to the present invention. Whilst the details are again not important for the present invention, we would say that the principal one of these circuitry applications is our International Patent Application No. PCT/GB2011/000920, which describes and claims (as published):
A power supply for a magnetron comprising:
                a DC voltage source;        a converter for raising the output voltage of the DC voltage source, the converter having:                    a capacitative-inductive resonant circuit,            a switching circuit adapted to drive the resonant circuit at a variable frequency above the resonant frequency of the resonant circuit, the variable frequency being controlled by a control signal input to provide an alternating voltage,            a transformer connected to the resonant circuit for raising the alternating voltage,            a rectifier for rectifying the raised alternating voltage to a raised DC voltage for application to the magnetron;                        means for measuring the current from the DC voltage source passing through the converter;        a microprocessor programmed to produce a control signal indicative of a desired output power of the magnetron; and        an integrated circuit arranged in a feed back loop and adapted to apply a control signal to the converter switching circuit in accordance with a comparison of a signal from the current measuring means with the signal from the microprocessor for controlling the power of the magnetron to the desired power.        
Whilst our LUWPL technology is in generally efficient in terms of lumens of light produced per watt of electricity consumed in its operation, they still dissipate a considerable wattage of heat that must be dissipated, to avoid components overheating. Magnetrons are particularly susceptible to overheating, significantly losing efficiency of microwave generation if their magnets are overheated.
Equally, we have sought to avoid use of cooling fans where possible in lamps using our LUWPL technology.
Conventionally magnetrons, particularly as used in microwave cookers, are cooled by forced air flow through a series of cooling fins attached to the anode of a magnetron. We are aware of a proposal to conduct heat from an anode for remote dissipation. This is in European Patent Application No 1,355,340, whose abstract is as follows:
Magnetron including a cylindrical anode (11) having a resonant space formed therein and a cathode fitted therein, magnets (12a,12b) fitted to upper and lower sides of the anode (11), a yoke (1) fitted on outsides of the anode (11) and the magnets (12a,12b) to form a closed circuit, and cooling devices including a main cooling device to form a heat discharge path from the anode (11), and a supplementary cooling device (60) to form a heat discharge path from the magnet (12b) direct or indirectly, wherein the main cooling device is an anode heat conductor (50) having one end closely fitted to an outside surface of the anode (11), and the other end passed to the yoke (1) and exposed to an external air, and the supplementary cooling device includes a magnet heat conductor (60) closely fitted to an outside surface of the magnet (12b), the magnet heat conductor (60); having one side in contact with the outside case (41) of the magnetron, or a yoke heat conductor (70) closely fitted to an outside surface of a yoke plate, the yoke heat conductor (70) having one side in contact with the outside case of the magnetron (41).